Allow splitting PLX NTB BAR2 into several memory windows.

Address Lookup Table (A-LUT) being enabled allows to specify separate
translation for each 1/128th or 1/256th of the BAR2. Previously it was
used only to limit effective window size by blocking access through some
of A-LUT elements. This change allows A-LUT elements to also point
different memory locations, providing to upper layers several (up to 128)
independent memory windows. A-LUT hardware allows even more flexible
configurations than this, but NTB KPI have no way to manage that now.

MFC after: 2 weeks
Sponsored by: iXsystems, Inc.